1. Field of the Invention
The present invention relates to a photoelectric converting device.
2. Related Background Art
In the conventional art of the photoelectric converting device, there is known for example a device of bipolar transistor type.
FIG. 8 shows, in a schematic cross-sectional view, an example of the conventional bipolar photoelectric converting device, in which there are provided a silicon substrate 1 of type by doping of an impurity such as phosphor (P), antimony (Sb) or arsenic (As) or a p type by doping of an impurity such as boron (B) or aluminum (Al); an n.sup.+ area 2 formed for example by an epitaxial process; an n-area 3 of a lower impurity concentration serving as a collector region; a p-area 4 serving as a light receiving base area for accumulating photo generated carries; an n.sup.+ -area 6 serving as an emitter; and an p.sup.+ area 7 serving as a channel stop or connected with the collector.
However, such a conventional photoelectric converting device has been associated with a drawback that the photosensitivity thereof is not always sufficient, and such drawback is more conspicuous in a miniatuarized photoelectric converting device.
In the conventional bipolar photoelectric converting device, the photosensitivity can be approximately represented as follows: ##EQU1## wherein i.sub.p is the photoinduced current density per unit area; A.sub.s is the aperture area; t.sub.s is the accumulation time; and C.sub.bc is the base-collector capacitance.
As will be apparent from the equation (1), the photosensitivity Se decreases with the increase of the base-collector capacitance C.sub.bc.